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Controlled comparison of humidified inhalation and peritoneal lavage in rewarming of immersion hypothermia
ControlledComparison of HumidifiedInhalation andPeritonealLavagein Rewarmingof ImmersionHypothermia J. DOUGLAS WHITE, MD,*t ARTHUR B. BUTTERFIELD, DVM, PhD,*$ TIMOTHY D. ALMQUIST, MD,* ROBERT R. HOLLOWAY, BS,*$ SCOTT SCHOEM, Random source dogs were anesthetized and cooled by immersion in ice water to a stable core temperature of 25°C and subsequently rewarmed with either normal saline peritoneal lavage (43% 175 ml/kg/h) or warmed humidified inhalation (43%, 450 ml/kg/min ventilation). The time required for core rewarming to 30°C was 192 -c 61 minutes for lavage and 331 + 96 minutes for inhalation therapy (P < 0.03). These data suggest that peritoneal lavage is superior to inhalation therapy for core rewarming of rapidly induced immersion hypothermia. (Am J Emerg Med 1964;2:210-214.)
The optimal clinical method for rewarming victims of accidental hypothermia has yet to be demonstrated. Although aggressive measures such as cardiopulmonary bypass, 1-3 mediastinal lavage,4*5 and hemodialysis6 are rapidly effective, these procedures are highly invasive and are not readily available in most emergency departments. Moreover, despite evidence that patients with core temperatures below 32°C are in imminent danger of spontaneous and often fatal ventricular dysrhythmias,’ some authors discourage therapeutic manipulation to avoid these same complications.2*8 Several studies support the superiority of active external rewarming for accidental hypothermia. The superiority of immersing the patient in warm baths has been described in theory9 and demonstrated in the laboratorylO,ll and clinically.12 Other studies, however, describe the superiority of active internal rewarming From the *School of Medicine, tDepartment of Emergency icine, and *Experimental Surgery Laboratory, Georgetown versity Medical Center, Washington, DC.
MedUni-
Supported by grants from the National Institutes of Health, Division of Research Resources (Biomedical Research Support Grant RR53601); Monatherm, Inc.; and Henry Medical Electronics. Manuscript 29, 1963.
received
June 27, 1963; revision
accepted
August
BS*$
in the treatment of hypothermia clinically13 and in the laboratory. 14*15 Furthermore, this confusion is only amplified by the conflicting data comparing the “afterwith internal and external redrop” experienced warming techniques. 14,15 The differences in technique used to cool and rewarm subjects, as well as the physical characteristics (species, size, and percentage of body fat), may explain much of this confusion. Until the present time, however, most physicians have used noninvasive core rewarming techniques for profound hypothermia because of their practical advantages. Bulky, expensive tub baths are not required, and access to and monitoring of the patient are not impeded. Moreover, the afterdrop phenomenon has been theoretically linked to premature vasodilation. The belief that circulation is causally involved in afterdrop has been challenged by the results of porcine experimentsI but conforms with observations made during surgical hypothermia and the knowledge that patients become volume depleted secondary to diuresis and fluid redistribution during slow-onset hypothermia.‘O The two most common, relatively noninvasive core rewarming techniques are inhalation therapy10%1’*1315,17,18 and peritoneal lavage.r9-24 In theory, peritoneal lavage should be able to transfer more heat than humidified inhalation.9 Myers et aP calculate that inhalation of warmed, humidified ventilation at 45°C and a minute ventilation of 300 ml/kg will transfer about 30 kcal/h, while peritoneal lavage at the same temperature and a flow rate greater than 60 ml/kg/h will transfer more heat. Despite their widespread clinical use, a direct comparison of these two methods under identical circumstances has not, to our knowledge, been conducted. In this paper, we report the results of a series of experiments assessing the comparative efficacy of these two methods of core rewarming for profound immersion hypothermia.
Address reprint requests to Dr. White: Department of Emergency Medicine, Georgetown University Medical Center, 3600 Reservoir Road, NW, Washington DC 20007.
MATERIALS
Key Words: Dialysis, rewarming.
Six random source mongrel dogs, each weighing between 15 and 24 kg, were shaved and given 0.04 mg/
210
hypothermia,
inhalation,
lavage, peritoneal,
AND METHODS
WHITE ET AL n IMMERSION HYPOTHERMIA
kg atropine sulfate subcutaneously as preanesthetic medication. Anesthesia was induced with an intravenous injection of thiamylal sodium (18 mg/kg). Following induction, the dogs were intubated with cuffed endotracheal tubes, and anesthesia with halothane, nitrous oxide, and oxygen was maintained at concentrations sufficient to prevent muscle fasciculation. The animals were connected to a volume ventilator (Air Shields Ventimeter, Hatboro, Pennsylvania), and respirations were controlled at lS/min with a tidal volume of 30 ml/kg. The studies were conducted in an environment free of extraneous sources of heating or cooling, and the animals were isolated from drafts and sunlight. The room temperature was monitored and maintained at 23 + 1.8”C. Continuous monitoring of electrocardiographic lead II and of room and core temperatures was done during all phases (preanesthesia, immersion, drift, and rewarming) of the experiment. The temperature measuring system consisted of thermocouples and a digital readout system (Model 6000, Monatherm, Inc., St. Louis, Missouri) with a system time constant of 8 seconds and an accuracy of O.l”C. The entire system was calibrated before each experiment. Probes were inserted in the descending colon (15 cm beyond the anus), the esophagus, and both ears of each dog. An esophageal stethoscope probe was installed at the point of maximum heart sound auscultation. Fine padded thermocouples were inserted, under direct otoscopic visualization, against the tympanic membranes. The ear canals were packed to seal against fluid leakage, and the pinnae were taped tightly shut. Each dog was then immersed in a prepared ice bath (0.8- 1.O”C), suspended by its limbs with the head and neck clear of the water. The animals were cooled to 28”C, removed from the bath and dried, and allowed to drift to 25°C core temperature. When they remained stable at this temperature for 10 minutes, the rewarming component of the experiment commenced. The dogs were randomly assigned to one of two treatment groups and subsequently rewarmed with peritoneal lavage or humidified inhalation. Seven days later, they were cooled and rewarmed with the alternative rewarming technique. Continuous infusion and drainage peritoneal lavage was performed under aseptic conditions. Fenestrated Bard catheters (28F, 19 cm) were inserted through a midline abdominal incision into the peritoneal cavity. The catheters were wrapped in sterile gauze to prevent blockage by the omentum, and the tips were situated dorsal to the small bowel and ventral to the aorta near the kidneys, Sterile normal saline was warmed, maintained at 43 + lXC, and infused into the abdominal cavity at a rate of 175 ml/kg/h by passage through a coil submerged in a hot water bath. Fluid temperature was monitored by a sterile thermocouple inserted into
the lumen of the catheter at the point of entry into the abdomen. Humidified inhalation was delivered to each animal by connecting the inspiratory flow tract of the breathing circuit in-line to a cascade humidifier (Bennett model #PN3010) filled with heated, sterile water to provide saturated, heated ventilation. The inspiratory tract bubbled through this reservoir. Temperature was constantly monitored by a thermocouple placed within the lumen of the endotracheal tube at the level of the dog’s incisor teeth and maintained at 43 ? 1.8”C. At the conclusion of the study, statistical analysis was performed on the data, utilizing the t-test by difference for paired data and assuming continuous data and normal distribution. This experiment was approved by the Animal Welfare Committee of the Georgetown University Medical Center. In conducting the research described here, the investigators adhered to the “Guide for Laboratory Animal Facilities and Care” as promulgated by the Committee for Laboratory Animal Resources, National Academy of Sciences National Research Council. RESULTS All dogs survived without sequelae, and no afterdrop phenomenon was observed with either rewarming modality. Sinus rhythms prevailed throughout the experiments in all dogs. The heart rates ranged between 25 and 110 beats/min and correlated with core temperature (i.e., the heart rate rose with the core temperature). The study findings were based upon the temperature values recorded by tympanic membrane thermocouples. Rectal temperature measurements are known to imperfectly reflect the temperatures of more critical core sites,25,26 and our experiments showed this to be true for the esophageal probe as well as with warm inhalation. Tympanic temperature measurements were consistent regardless of the rewarming method employed, an observation corroborated by many other investigators.i1*15*27,2*Moreover, the presence of bilateral probes provided independently calibrated readings and insurance against failure of probes or leakage of water into the ear canal. The study data are presented in a scatter diagram (Fig. 1) showing the effect of rewarming on tympanic temperature over time. Figure 2 shows the difference in rewarming time for the two techniques. Peritoneal lavage therapy (mean 193 ? 56 min) warmed the animals more rapidly than inhalation (mean 332 2 88 min), and this difference in rewarming times (60-315 min) was statistically significant at the P < 0.03 level. Rewarming rates for either modality were unaffected by sex or amount of body fat. 211
AMERICAN JOURNAL OF EMERGENCY MEDICINE n Volume 2, Number 3 W May 1984
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Minutes FIGURE 1.
Comparison of inhalation and lavage in rewarming of hypothermic
The total cooling times varied considerably (95 + 25 min), largely as a result of the time required for the animals’ temperature to drift from 28 to 25°C (63 & 45 min). Dogs with cooling times above the median (109 min) took longer to rewarm with both therapies, and this difference was statistically significant for inhalation. However, increased cooling time was largely associated with size of the animal, and when the two large dogs (>20 kg) were not considered, cooling time did not affect either modality. These larger animals took longer to cool (129 f 9 versus 80 + 23 min) and rewarm with inhalation (443 + 25 versus 276 & 53 min, P < 0.04). DISCUSSION Our experiments indicate that under laboratory conditions, peritoneal lavage is superior to warmed, humidified inhalation as a means for rewarming hypothermic dogs. The difference between lavage and inhalation rewarming times was statistically significant for the overall group of dogs, regardless of sex or body fat, and was more pronounced for larger animals. Clinically, utilization of the faster lavage method could be important, given that core temperatures in the 25-32°C range predispose to spontaneous and fatal arrhythmias.7 While differences of physiology and size 212
dogs. (0 = lavage; 0 = inhalation.)
between dogs and human beings prevent precise extrapolation of our findings to the clinical setting, it is possible that humans may benefit from lavage even more, as the superiority of this technique was most evident in the larger animals. Moreover, although our experiments dealt specifically with immersion-induced hypothermia, the relative efficacy and efficiency of the two rewarming methods should obtain in other forms of hypothermia. Because each trial had to be completed within an eight-hour period for logistical reasons, a 30°C endpoint was selected. Therefore, the efficacy of the two treatments for core temperatures above the 25-30°C range should also be considered. While the relative efficacy of lavage may be diminished at higher temperatures, nothing in our data suggests that rewarming rates for the two modalities would equalize. Furthermore, the work of other investigators indicates that active core rewarming is generally not necessary beyond 30-32”C.7,19 The temperatures of lavage fluid and inhalation therapy used in this experiment conform to the highest figures given in the literature14*‘5*‘9~20 and human tolerance.” A dialysis flow rate of 175 ml/kg/h was selected to conform with the highest reported rates for peritoneal lavage rewarming in accidental hypothermia. 19+20 In
WHITE ET AL n IMMERSION
I
I
I
I
I
150
225
300
375
450
HYPOTHERMIA
Minutes FIGURE 2. Comparative rates of rewarming for hypothermic dogs treated with lavage or inhalation. (O-O-O inhalation. Dots represent mean values; bars iepresknt 2 1 SD.)
order to attain these flow rates in our study, we used large catheters to deliver fluid into the dog’s abdominal cavity. Also, the catheter fenestrations were wrapped with gauze to prevent the dog’s generoussized omentum from occluding the tube outlet. The lavage flow rates used in our experiments may be difficult to achieve clinically. Extrapolation of our flow rates to a 70 kg man would require rates in excess of 12 l/h. The achievement of such rates clinically, in patients, would require two affluent catheters; suction outflow through a third, effluent catheter;19 and close supervision. Flow rates of 6 l/h are more plausible clinically,2’*23and at this reduced rate, inhalation therapy may be comparable to lavage. Although the temperatures of peritoneal effluent and expired air were not measured, it appears that the efficiency of heat transfer was considerably greater for inhalation than for lavage. If the calculations of Myers et al9 are used, a dog at 25°C receiving a saline infusion at 43°C and at 175 ml/kg/h receives a potential heat transfer of (43-25) kcal/ml x 175 ml/kg/h, or 3.10 kcal/ kg/h, The total heat of water-saturated air at 25°C is 14.5 Cal/l, and at 43°C 32.62 cal/L9 Accordingly, our inhalation protocol could deliver a potential (36.6214.5) cal/l x 0.45 l/mm/kg x 60 mm/h, or 0.6 kcal/kg/ h, of heat.
= lavage; 0 . . 0 . . 0 =
Theoretically, then, lavage should have delivered over five times the heat of inhalation. The fact that lavage rewarming was only 40% more rapid in our experiments suggests that humidified inhalation may be a considerably more efficient means of heat transfer. The use of a continuous infusion and drainage system for lavage kept temperature transfer gradients high, and while this improved the rate of heat transfer, the limited dwell time undoubtedly undermined the efftciency of heat transfer. Under ideal laboratory conditions, aggressive peritoneal lavage proved to be significantly more rapid than warm humidified inhalation for rewarming canine victims of severe immersion hypothermia. Under clinical conditions in human beings, however, lavage may be technically more difficult and invasive, diminishing the advantages demonstrated in our studies. REFERENCES 1. Towne WD, Geiss WP, Yanes HO, et al. Intractable ventricular fibrillation associated with profound accidental hypothermia-Successful treatment with partial cardiopulmonary bypass. N Engl J Med 1972;267:1135-1136. 2. Wickstrom P, Ruiz E, Lilja GP, et al. Accidental hypothermia treated with partial bypass. Am J Surg 1976;131:622-625. 3. Dorsey JS. Venoarterial bypass in hypothermia. JAMA 1980;244:1900. 213
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JOURNAL
OF EMERGENCY
MEDICINE
n Volume 2, Number 3 n May 1984
4. Coughlin F. Heart-rewarming procedure. N Engl J Med 1973;288:326. 5. Linton AL, Ledingham I. Severe hypothermia with barbiturate intoxication. Lancet 1966;i :24-26. 6. Lee HA, Ames AC. Hemodialysis in severe barbiturate poisoning. Br Med J 1965;1:1217-1219. 7. White JD. Hypothermia: The Bellevue experience. Ann Emerg Med 1982;11:417-424. 8. O’Keefe KM. Accidental hypothermia: A review of 62 cases. JACEP 1977;6:491-496. 9. Myers RA, Britten JS, Cowley RA. Hypothermia: Quantitative aspects of therapy. JACEP 1979;8:523-527. 10. Harnett RM, O’Brien EM, Sias FR, et al. Initial treatment of profound accidental hypothermia. Aviat Space Environ Med 1980;51:680-687. 11. Marcus P. Laboratory warming hypothermic Med 1978;49:692-697.
comparison casualties.
of techniques Aviat Space
for reEnviron
12. Zachary LJ, Kucan JO, Robson MC, et al. Accidental hypothermia trea?ed with rapid rewarming by immersion. Ann Plast Surg 1982;9:239-240.
17. 18.
19.
20.
21. 22. 23. 24.
25.
13. Miller JW, Danzl DF, Thomas DM. Urban accidental hypothermia: 135 cases. Ann Emerg Med 1980;9:456-461.
26.
14. Collis ML, Steinman AM, Chavey RD. Accidental hypothermia: An experimental study of practical rewarming methods. Aviat Space Environ Med 1977;48:625-632.
27.
15. Hayward JS, Steinman AM. Accidental hypothermia: An experimental study of inhalation rewarming. Aviat Space Environ Med 1975;46:1236-1240. 16. Golden F, Hervey GR. The mechanism of the after-drop fol-
214
28.
lowing immersion hypothermia in pigs. J Physiol 1977;272:26-27. Edsall DW. Treatment of hypothermia. JAMA 1980;244:1902. Lloyd EL. Accidental hypothermia treatment by central rewarming through the airway. Br J Anaesth 1973;45: 41-48. Jessen K, Hagelstem JO. Peritoneal dialysis in the treatment of profound accidental hypothermia. Aviat Space Environ Med 1978;49:426-429. Patton JF, Doolittle WH. Core rewarming by peritoneal dialysis following induced hypothermia in the dog. J Appl Physiol 1974;33:800-804. Johnson LA. Accidental hypothermia: Peritoneal dialysis. JACEP 1977;6:556-561. Reuler JB, Parker RA. Peritoneal dialysis in the management of hypothermia. JAMA 1978;240:2289-2290. Grossheim RL. Hypothermia and frostbite treated with peritoneal dialysis. Alaska Med 973;15:53-55. Southwick FS, Daglish PH Jr. Recovery after prolonged asystolic cardiac arrest in profound hypothermia. JAMA 1980;243:1250-1253. Wilson RD, Knapp C, Traber DL. Tympanic thermography. South Med J 1971;64:1452-1455. Edwards RJ, Belyavin AJ, Harrison MH. Core temperature measurement for man. Aviat Space Environ Med 1978;49:1289-1294. Webb GE. Comparison of esophageal and tympanic temperature monitoring during cardiopulmonary bypass. Anesth Analg (Cleve) 1973;52:729-733. Wilson RD, Knapp C, Traber DL. Tympanic thermography. South Med J 1971;64:1452-1455.
The optimal clinical method for rewarming victims of accidental hypothermia has yet to be demonstrated. Although aggressive measures such as cardiopulmonary bypass, 1-3 mediastinal lavage,4*5 and hemodialysis6 are rapidly effective, these procedures are highly invasive and are not readily available in most emergency departments. Moreover, despite evidence that patients with core temperatures below 32°C are in imminent danger of spontaneous and often fatal ventricular dysrhythmias,’ some authors discourage therapeutic manipulation to avoid these same complications.2*8 Several studies support the superiority of active external rewarming for accidental hypothermia. The superiority of immersing the patient in warm baths has been described in theory9 and demonstrated in the laboratorylO,ll and clinically.12 Other studies, however, describe the superiority of active internal rewarming From the *School of Medicine, tDepartment of Emergency icine, and *Experimental Surgery Laboratory, Georgetown versity Medical Center, Washington, DC.
MedUni-
Supported by grants from the National Institutes of Health, Division of Research Resources (Biomedical Research Support Grant RR53601); Monatherm, Inc.; and Henry Medical Electronics. Manuscript 29, 1963.
received
June 27, 1963; revision
accepted
August
BS*$
in the treatment of hypothermia clinically13 and in the laboratory. 14*15 Furthermore, this confusion is only amplified by the conflicting data comparing the “afterwith internal and external redrop” experienced warming techniques. 14,15 The differences in technique used to cool and rewarm subjects, as well as the physical characteristics (species, size, and percentage of body fat), may explain much of this confusion. Until the present time, however, most physicians have used noninvasive core rewarming techniques for profound hypothermia because of their practical advantages. Bulky, expensive tub baths are not required, and access to and monitoring of the patient are not impeded. Moreover, the afterdrop phenomenon has been theoretically linked to premature vasodilation. The belief that circulation is causally involved in afterdrop has been challenged by the results of porcine experimentsI but conforms with observations made during surgical hypothermia and the knowledge that patients become volume depleted secondary to diuresis and fluid redistribution during slow-onset hypothermia.‘O The two most common, relatively noninvasive core rewarming techniques are inhalation therapy10%1’*1315,17,18 and peritoneal lavage.r9-24 In theory, peritoneal lavage should be able to transfer more heat than humidified inhalation.9 Myers et aP calculate that inhalation of warmed, humidified ventilation at 45°C and a minute ventilation of 300 ml/kg will transfer about 30 kcal/h, while peritoneal lavage at the same temperature and a flow rate greater than 60 ml/kg/h will transfer more heat. Despite their widespread clinical use, a direct comparison of these two methods under identical circumstances has not, to our knowledge, been conducted. In this paper, we report the results of a series of experiments assessing the comparative efficacy of these two methods of core rewarming for profound immersion hypothermia.
Address reprint requests to Dr. White: Department of Emergency Medicine, Georgetown University Medical Center, 3600 Reservoir Road, NW, Washington DC 20007.
MATERIALS
Key Words: Dialysis, rewarming.
Six random source mongrel dogs, each weighing between 15 and 24 kg, were shaved and given 0.04 mg/
210
hypothermia,
inhalation,
lavage, peritoneal,
AND METHODS
WHITE ET AL n IMMERSION HYPOTHERMIA
kg atropine sulfate subcutaneously as preanesthetic medication. Anesthesia was induced with an intravenous injection of thiamylal sodium (18 mg/kg). Following induction, the dogs were intubated with cuffed endotracheal tubes, and anesthesia with halothane, nitrous oxide, and oxygen was maintained at concentrations sufficient to prevent muscle fasciculation. The animals were connected to a volume ventilator (Air Shields Ventimeter, Hatboro, Pennsylvania), and respirations were controlled at lS/min with a tidal volume of 30 ml/kg. The studies were conducted in an environment free of extraneous sources of heating or cooling, and the animals were isolated from drafts and sunlight. The room temperature was monitored and maintained at 23 + 1.8”C. Continuous monitoring of electrocardiographic lead II and of room and core temperatures was done during all phases (preanesthesia, immersion, drift, and rewarming) of the experiment. The temperature measuring system consisted of thermocouples and a digital readout system (Model 6000, Monatherm, Inc., St. Louis, Missouri) with a system time constant of 8 seconds and an accuracy of O.l”C. The entire system was calibrated before each experiment. Probes were inserted in the descending colon (15 cm beyond the anus), the esophagus, and both ears of each dog. An esophageal stethoscope probe was installed at the point of maximum heart sound auscultation. Fine padded thermocouples were inserted, under direct otoscopic visualization, against the tympanic membranes. The ear canals were packed to seal against fluid leakage, and the pinnae were taped tightly shut. Each dog was then immersed in a prepared ice bath (0.8- 1.O”C), suspended by its limbs with the head and neck clear of the water. The animals were cooled to 28”C, removed from the bath and dried, and allowed to drift to 25°C core temperature. When they remained stable at this temperature for 10 minutes, the rewarming component of the experiment commenced. The dogs were randomly assigned to one of two treatment groups and subsequently rewarmed with peritoneal lavage or humidified inhalation. Seven days later, they were cooled and rewarmed with the alternative rewarming technique. Continuous infusion and drainage peritoneal lavage was performed under aseptic conditions. Fenestrated Bard catheters (28F, 19 cm) were inserted through a midline abdominal incision into the peritoneal cavity. The catheters were wrapped in sterile gauze to prevent blockage by the omentum, and the tips were situated dorsal to the small bowel and ventral to the aorta near the kidneys, Sterile normal saline was warmed, maintained at 43 + lXC, and infused into the abdominal cavity at a rate of 175 ml/kg/h by passage through a coil submerged in a hot water bath. Fluid temperature was monitored by a sterile thermocouple inserted into
the lumen of the catheter at the point of entry into the abdomen. Humidified inhalation was delivered to each animal by connecting the inspiratory flow tract of the breathing circuit in-line to a cascade humidifier (Bennett model #PN3010) filled with heated, sterile water to provide saturated, heated ventilation. The inspiratory tract bubbled through this reservoir. Temperature was constantly monitored by a thermocouple placed within the lumen of the endotracheal tube at the level of the dog’s incisor teeth and maintained at 43 ? 1.8”C. At the conclusion of the study, statistical analysis was performed on the data, utilizing the t-test by difference for paired data and assuming continuous data and normal distribution. This experiment was approved by the Animal Welfare Committee of the Georgetown University Medical Center. In conducting the research described here, the investigators adhered to the “Guide for Laboratory Animal Facilities and Care” as promulgated by the Committee for Laboratory Animal Resources, National Academy of Sciences National Research Council. RESULTS All dogs survived without sequelae, and no afterdrop phenomenon was observed with either rewarming modality. Sinus rhythms prevailed throughout the experiments in all dogs. The heart rates ranged between 25 and 110 beats/min and correlated with core temperature (i.e., the heart rate rose with the core temperature). The study findings were based upon the temperature values recorded by tympanic membrane thermocouples. Rectal temperature measurements are known to imperfectly reflect the temperatures of more critical core sites,25,26 and our experiments showed this to be true for the esophageal probe as well as with warm inhalation. Tympanic temperature measurements were consistent regardless of the rewarming method employed, an observation corroborated by many other investigators.i1*15*27,2*Moreover, the presence of bilateral probes provided independently calibrated readings and insurance against failure of probes or leakage of water into the ear canal. The study data are presented in a scatter diagram (Fig. 1) showing the effect of rewarming on tympanic temperature over time. Figure 2 shows the difference in rewarming time for the two techniques. Peritoneal lavage therapy (mean 193 ? 56 min) warmed the animals more rapidly than inhalation (mean 332 2 88 min), and this difference in rewarming times (60-315 min) was statistically significant at the P < 0.03 level. Rewarming rates for either modality were unaffected by sex or amount of body fat. 211
AMERICAN JOURNAL OF EMERGENCY MEDICINE n Volume 2, Number 3 W May 1984
30
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0 .
e-0 0
:” .
.
OI . . 0
25’
1 75
1 150
I 225
1 300
1 375
I 450
Minutes FIGURE 1.
Comparison of inhalation and lavage in rewarming of hypothermic
The total cooling times varied considerably (95 + 25 min), largely as a result of the time required for the animals’ temperature to drift from 28 to 25°C (63 & 45 min). Dogs with cooling times above the median (109 min) took longer to rewarm with both therapies, and this difference was statistically significant for inhalation. However, increased cooling time was largely associated with size of the animal, and when the two large dogs (>20 kg) were not considered, cooling time did not affect either modality. These larger animals took longer to cool (129 f 9 versus 80 + 23 min) and rewarm with inhalation (443 + 25 versus 276 & 53 min, P < 0.04). DISCUSSION Our experiments indicate that under laboratory conditions, peritoneal lavage is superior to warmed, humidified inhalation as a means for rewarming hypothermic dogs. The difference between lavage and inhalation rewarming times was statistically significant for the overall group of dogs, regardless of sex or body fat, and was more pronounced for larger animals. Clinically, utilization of the faster lavage method could be important, given that core temperatures in the 25-32°C range predispose to spontaneous and fatal arrhythmias.7 While differences of physiology and size 212
dogs. (0 = lavage; 0 = inhalation.)
between dogs and human beings prevent precise extrapolation of our findings to the clinical setting, it is possible that humans may benefit from lavage even more, as the superiority of this technique was most evident in the larger animals. Moreover, although our experiments dealt specifically with immersion-induced hypothermia, the relative efficacy and efficiency of the two rewarming methods should obtain in other forms of hypothermia. Because each trial had to be completed within an eight-hour period for logistical reasons, a 30°C endpoint was selected. Therefore, the efficacy of the two treatments for core temperatures above the 25-30°C range should also be considered. While the relative efficacy of lavage may be diminished at higher temperatures, nothing in our data suggests that rewarming rates for the two modalities would equalize. Furthermore, the work of other investigators indicates that active core rewarming is generally not necessary beyond 30-32”C.7,19 The temperatures of lavage fluid and inhalation therapy used in this experiment conform to the highest figures given in the literature14*‘5*‘9~20 and human tolerance.” A dialysis flow rate of 175 ml/kg/h was selected to conform with the highest reported rates for peritoneal lavage rewarming in accidental hypothermia. 19+20 In
WHITE ET AL n IMMERSION
I
I
I
I
I
150
225
300
375
450
HYPOTHERMIA
Minutes FIGURE 2. Comparative rates of rewarming for hypothermic dogs treated with lavage or inhalation. (O-O-O inhalation. Dots represent mean values; bars iepresknt 2 1 SD.)
order to attain these flow rates in our study, we used large catheters to deliver fluid into the dog’s abdominal cavity. Also, the catheter fenestrations were wrapped with gauze to prevent the dog’s generoussized omentum from occluding the tube outlet. The lavage flow rates used in our experiments may be difficult to achieve clinically. Extrapolation of our flow rates to a 70 kg man would require rates in excess of 12 l/h. The achievement of such rates clinically, in patients, would require two affluent catheters; suction outflow through a third, effluent catheter;19 and close supervision. Flow rates of 6 l/h are more plausible clinically,2’*23and at this reduced rate, inhalation therapy may be comparable to lavage. Although the temperatures of peritoneal effluent and expired air were not measured, it appears that the efficiency of heat transfer was considerably greater for inhalation than for lavage. If the calculations of Myers et al9 are used, a dog at 25°C receiving a saline infusion at 43°C and at 175 ml/kg/h receives a potential heat transfer of (43-25) kcal/ml x 175 ml/kg/h, or 3.10 kcal/ kg/h, The total heat of water-saturated air at 25°C is 14.5 Cal/l, and at 43°C 32.62 cal/L9 Accordingly, our inhalation protocol could deliver a potential (36.6214.5) cal/l x 0.45 l/mm/kg x 60 mm/h, or 0.6 kcal/kg/ h, of heat.
= lavage; 0 . . 0 . . 0 =
Theoretically, then, lavage should have delivered over five times the heat of inhalation. The fact that lavage rewarming was only 40% more rapid in our experiments suggests that humidified inhalation may be a considerably more efficient means of heat transfer. The use of a continuous infusion and drainage system for lavage kept temperature transfer gradients high, and while this improved the rate of heat transfer, the limited dwell time undoubtedly undermined the efftciency of heat transfer. Under ideal laboratory conditions, aggressive peritoneal lavage proved to be significantly more rapid than warm humidified inhalation for rewarming canine victims of severe immersion hypothermia. Under clinical conditions in human beings, however, lavage may be technically more difficult and invasive, diminishing the advantages demonstrated in our studies. REFERENCES 1. Towne WD, Geiss WP, Yanes HO, et al. Intractable ventricular fibrillation associated with profound accidental hypothermia-Successful treatment with partial cardiopulmonary bypass. N Engl J Med 1972;267:1135-1136. 2. Wickstrom P, Ruiz E, Lilja GP, et al. Accidental hypothermia treated with partial bypass. Am J Surg 1976;131:622-625. 3. Dorsey JS. Venoarterial bypass in hypothermia. JAMA 1980;244:1900. 213
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